Have a look at these for starters .....
Mac Switching 101
Mac 101
MacTricksAndTips ~ 100 Essential Mac Apps
Mac OS Menu Bar Items
Mac OS Keyboard Shortcuts
Mac downloads ~ Apple
Here is a list of Apps that people around here use a lot, but be sure to check out what came with the Mac as they are really sufficient in doing most things
Adium ~ Chat Client
Growl Notifications
SuperDuper or CarbonCopyCloner ~ Both make bootable copies of your HD
HandBrake ~ Video Converting
Burn ~ As it says A Burning App
Transmission ~ p2p client
Skitch ~ Screen capture and more
VLC ~ Video player that plays most codecs and does a lot more
Perian and
Flip4Mac Makes watching certain codecs easier ... This is Essential IMHO
Audacity ~ Play with Music App
CandyBar ~ Mods all your icons, and dock
MainMenu or
Oynx ~ Does the same as Disk utility only more thorough
Quicksilver ~ Works like Spotlight but way way better and does so much more
StuffitExpander ~ Opens Zip and rar files and more
Lil Snitch ~ Firewall type App that looks at your incoming and outgoing traffic
and last but certainly not least .....
AppTrap ~ Once installed it sits in System Preferences and deletes all associated files of anything that you put in the trash ...
Should keep you busy for a while lol
HTH
Cheers